Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $64.46   11.407%   $71.813   $71.81   $71.80   $71.80  
  Purchase #2 $112.65   5.665%   $119.0316   $119.03   $119.05   $119.00  
  Purchase #3 $158.63   11.837%   $177.407   $177.41   $177.40   $177.40  
  Purchase #4 $212.90   9.289%   $232.6763   $232.68   $232.70   $232.70  
  Purchase #5 $140.80   13.420%   $159.6954   $159.70   $159.70   $159.70  
  Purchase #6 $161.44   3.786%   $167.5521   $167.55   $167.55   $167.60  
  Purchase #7 $57.41   12.867%   $64.7969   $64.80   $64.80   $64.80  
  7 purchase totals = $908.29       $992.9723   $992.98   $993.00   $993.00